A typical cylindrical, cartridge-type fluid processing apparatus may comprise a hollow, generally cylindrical, permeable filter cartridge disposed within a housing. The housing typically includes two or more portions which are joined together about the filter cartridge. In conventional embodiments, the filter cartridge is pre-assembled to include a cage about the exterior, a core disposed on the interior, a tubular porous element disposed between the core and the cage, and first and second end caps holding the core, cage, and porous element together. The end-caps may be sealed to the ends of the porous element using an adhesive, welding, or a annular knife-edge which penetrates into the porous element. The housing may then be sealed to the end caps using, for example, one or more resilient O-rings. Typically, the housing includes a seat mechanism to compress the O-ring seals.
A problem arises with conventional cartridge-type fluid processing apparatuses in that a large number of components and manufacturing steps are required which increases the cost and reduces the overall reliability of the fluid processing apparatus. Further, conventional cartridge-type filters may have impurities from an adhesive or O-ring seal leach into the filtrate. This can be particularly serious when filtering fluids used in a semiconductor manufacturing process. Additionally, with some configurations and applied pressures, the filter cartridge may distend, distort, rupture, or even burst, thereby reducing the efficiency and/or reliability of the filter.
Additionally, a potentially costly problem associated with the use of any filter assembly is the problem of hold-up volume waste. When a filter element must be replaced, typically during routine maintenance, a portion of the fluid remains within the filter element housing. The remaining fluid generally cannot be reused due to possible contamination; therefore, this excess fluid must be disposed of, and depending upon the fluid, the replacement of the fluid can be costly. For example, in the integrated circuit industry, photo lithography is a technique utilized in various mask work procedures. Photoresist is a light sensitive chemical mixture which is used in photo lithography. In the photo lithography procedure, the photoresist is pumped onto a spinning disc which spreads the viscous photoresist over the particular work product. The pump assembly utilized has a filter housing that accepts a small disposable filter which must be replaced periodically and excess photoresist in the filter housing is lost. A typical positive photoresist can cost up to six hundred dollars or more per gallon, making waste extremely costly. In addition to the direct cost of replacing the wasted fluid, there is the cost of disposal. There are environmental factors which need to be considered in the disposal of certain chemicals, thereby making disposal as potentially costly as buying new chemicals.